The present invention relates to an improved photohardenable light-sensitive composition of the type including a light-sensitive silver halide, a developing agent, and a polymerizable compound wherein the composition further includes a coumarin or a ketocoumarin. It has been found that the coumarin or ketocoumarin reduces Dmin, improves the Dmax/Dmin ratio, increases the developing latitude of the composition, and improves image sharpness.
Light-sensitive compositions comprising a silver halide, a developing agent, and a polymerizable compound are known in the art. The compositions are image-wise exposed to form a latent image and then heated to polymerize the polymerizable compound. Depending upon the nature of the silver halide and the developer, the composition may be hardened in exposed or unexposed areas. These light-sensitive compositions are the subject of the following European Patent Publication Nos.: 0 203 613; 0 228 083; 0 234 580; and 0 228 053. European application No. 0 203 613 specifically relates to a photosensitive material in which the compositions are micro encapsulated with an image-forming agent.
One of the drawbacks of the aforementioned light-sensitive compositions is that they exhibit a comparatively high background density or Dmin. Another is that there can be significant variations in the quality of the images obtained with variations in the heating conditions used in developing the image. As the compositions are heated for increasing periods of time higher temperatures to polymerize the polymerizable compound, there is a reduction in sharpness and Dmax is observed to fall off rapidly. As a consequence of the high Dmin and falling Dmax, there is a very narrow window in which the materials can be heated to provide the maximum ratio of Dmax to Dmin. This detracts from the utility of the compositions.